Mac Pro wont startup with GTX970 Graphics Card (for DaVinci Resolve)

This might not be the right place to post this question, but I am not sure where else to put it so I put it here.

To work in DaVinci Resolve I bought a "Gainward GeForce GTX970 4GB Phantom" Graphics card PC-version
Being told that the only difference from a PC-version and Mac-version would be that I dont get the Apple Boot Screen.
Is that so?

What happens when I install the card is that the Mac seemingly boot up, it goes a little time (30-60 seconds) and then it restarts and the same process goes again and again. Never getting anything on the screen.

I can not continue to use my my current card as UI since it also requires extra power connected.

I have installed both (2x) Power chords on the GTX970 graphics card.
Is there something else I should do/haven't done?
Do I need another driver?

[Øystein Rabbe]"What happens when I install the card is that the Mac seemingly boot up, it goes a little time (30-60 seconds) and then it restarts and the same process goes again and again. Never getting anything on the screen."

Yes, that means that you don't have an appropriate driver and the OS boot doesn't think you have a GPU installed. Are you trying to run Resolve on the GTX970 inside the Mac? That will be a power concern.

Try looking for an nVidia driver like 346.02.03f05 which is what I am currently driving my Titan Blacks with under Yosemite.

jPo

"I always pass on free advice -- its never of any use to me" Oscar Wilde.